This invention relates to an-apparatus for electrophoresis for analyzing an extremely small amount of protein and nucleic acid. More particularly, the invention relates to an apparatus for electrophoresis using either a capillary or a microchip having a groove formed between a pair of transparent planar members and separating sample components therein by electrophoresis.
Apparatus for electrophoresis with a capillary have been largely in use for analyzing extremely small amounts of protein and nucleic acids. When such an apparatus with a capillary is used, a sample is injected from one end of the capillary and a voltage difference for electrophoresis is applied between the end points of the capillary to cause the sample to migrate inside.
Recently, however, apparatus for electrophoresis having a microchip instead of a capillary are coming to be used. As shown in FIGS. 1A, 1B and 1C, a microchip 5 is formed by pasting together a pair of transparent base plates (the xe2x80x9cupper plate 51xe2x80x9d and the xe2x80x9clower plate 52xe2x80x9d ), say, made of a glass material. The lower plate 52 has mutually crossing capillary grooves (the xe2x80x9cshorter groove 54xe2x80x9d and the xe2x80x9clonger groovexe2x80x9d 55) formed on its surface for a migrating liquid to travel through, while the upper plate 51 has reservoirs 53 formed as throughholes at positions corresponding to the end points of the grooves 54 and 55.
The microchip 5 is formed by superposing the two base plates 51 and 52 as shown in FIG. 1C, and a liquid for electrophoresis is injected into the grooves 54 and 55 through any one of the reservoirs 53. Thereafter, a sample is injected into a reservoir 53 at either end of the shorter groove 54 and a high voltage is applied for a specified period of time between the ends of this groove 54 by inserting electrodes into the reservoirs 53 at both ends of the shorter groove 54. The sample is thereby caused to travel through the groove 54. Next, electrodes are inserted into the reservoirs 53 at both ends of the longer groove 55 and a voltage difference for electrophoresis is applied therebetween. This causes the portion of the sample at the crossing point 56 of the grooves 54 and 55 to migrate along the longer groove 55.
For detecting components of a sample, it has been a common practice to place a detector such as an ultraviolet/visible light spectrophotometer, a fluorescence photometer or an electrochemical detector along the flow route of the sample. Japanese Patent publication Tokkai 10-132783 has disclosed a different method of detection whereby a beam of light is made incident over a specified area along the flow route and an optical detector having a plurality of light-receiving elements disposed along the flow route is used to simultaneously detect the absorption or emission of light from the sample components separated inside the flow route over a specified range of distance therealong.
The migration pattern of sample components separated by an electrophoresis apparatus is usually displayed in the form of an electropherogram, showing absorption or intensity of emitted light by each component along the flow route for the separation. The pattern, however, may also be displayed as a gel image, showing the separated sample components as a band pattern along the flow route.
When the display is over a specified range of distance along the flow route for the separation, whether it is by way of an electropherogram or a gel image, the display is made as of a time by which the separation of the sample by electrophoresis has been completed. As long as the electrophoresis is carried out for the purpose of a quantitative analysis of protein or a nucleic acid, it is sufficient to display a pattern after the separation has been completed. According to a method of detection whereby a detector is placed at an appropriate position along the flow route for the separation for detecting the sample components as they pass, in particular, the sample components are displayed against a time axis and it is not a display of the entire migration pattern which changes constantly from one time to another along the flow route, although this is sometimes referred to as a real-time display.
Although an electropherogram and a gel image may both be displayed, not only is the display made after the separation by electrophoresis has been completed, but also the display is not made with the coordinate axes used in common. Such a display is not required if quantitative analysis is the only object.
It has been noted, however, that there are situations where it is desirable to ascertain the migration pattern not only after the separation has been completed but also during the course of the separation by electrophoresis. Such a situation comes about, for example, when the operator has noted an abnormal migration occurring between the start and the completion of electrophoresis. In such a situation, it is believed that the overall understanding of the migration pattern can be more easily obtained if the migration pattern during the course of migration is displayed as a gel image rather than as an electropherogram. It has never been done, however, to display the pattern during the course of migration as a gel image.
It is therefore an object of this invention, in view of the above, to provide an apparatus for electrophoresis capable of displaying a migration pattern during the course of migration of sample components as a gel image.
An apparatus for electrophoresis embodying this invention, with which the above and other objects can be accomplished, may be characterized as comprising not only a transparent device for electrophoresis such as a microchip or a capillary having a flow route, a power source for applying a voltage difference between end points of the flow route, an irradiating device for irradiating a specified portion of the flow route with light and an optical detector having a plurality of light-receiving elements arranged along the flow route for detecting absorption or emission of light by sample components separated in the flow route, but also a display device and a control unit for causing the display device to display data on the sample components separated in the flow route as a gel image based on detection signals from the optical detector while electrophoresis is being carried out by the apparatus. The gel image is for showing the sample components in a band form along the flow route, and the display device may also be adapted to display an electropherogram, showing absorptivity of light by or intensity of emitted light from the separated sample components along the flow route based also on the detection signals. Both the electropherogram and the gel image may show positions along the flow route in common.